Liquid developer dispersions are known in the art and are used for electrophotography and developing electrostatic latent images formed on a latent image carrying member in a digital printing process. An example of such printing apparatus is provided in U.S. Pat. No. 7,995,953, the content of which is incorporated into this application in its entirety by reference.
A digital printing apparatus using liquid developer dispersion is often provided with means to collect excess liquid developer dispersion. Excess liquid developer dispersion is liquid developer dispersion that remains on a member and that is not transferred to the substrate during the printing process. The collected excess liquid developer dispersion can be recycled and can be reused. A problem of the known liquid developer dispersions is that the excess liquid developer dispersion remaining on the developer roll has a tendency to show caking. Caking is the formation of lumps in the dispersion resulting in a liquid where there is no uniform dispersion of the marking particles. Caking often results in an increase of viscosity of the liquid. Caking in liquid developer dispersion is the process where marking particles are no longer evenly dispersed in the carrier liquid and are not acting anymore as individual particles. Liquid developer dispersion that shows caking cannot be used for printing as such and needs to be treated first in order to re-obtain a homogeneously dispersed liquid toner which has similar conductivity and viscosity properties as the starting liquid developer dispersion. It is thought that caking is the result of marking particles that come so close into each other's neighborhood on the developing member, so that they start to feel each other's presence and start interacting with each other. Caking can also be the result of injecting charge and applying high shearing forces which are typically present when a thin layer of liquid developer dispersion passes through a very narrow gap between two members of the printing apparatus.
It is an object of the invention, amongst other objects, to provide excess liquid developer dispersion with reduced or no caking.
It is another object of the invention to reduce caking in excess liquid developer dispersion, so that it can be reused as such, or can be reused by applying only a small number of steps required for obtaining a homogenously dispersed liquid developer dispersion.
These objects, amongst other objects, are met at least partially, if not completely by various embodiments of this invention.
For example, these objects, amongst other objects, are met at least partially, if not completely by a method for the reduction of caking of excess liquid developer dispersion that remains present on the surface of a member after transfer of liquid developer dispersion from one member to another member in a digital printing apparatus, comprising the step of adding a dispersing composition to the excess liquid developer dispersion, wherein the dispersing composition comprises a dispersing agent. The dispersing agent is added with an amount that is sufficient to provide a reduction of caking